328 KING. [Vol. XVII. 



much pigment could be torn from the peripheral layer without 

 leaving the place where the sperm entered nearly devoid of 

 pigment granules, and yet this region does not appear to have 

 lost any of its pigment. Again, if Hertwig's view is correct, 

 there should be a large amount of pigment around the enter- 

 ing sperm, which should steadily decrease as the sperm pene- 

 trates deeper into the egg ; but according to Pick's Fig. 2^, 

 the sperm-head, very soon after entering the Qgg, has almost no 

 pigment around it. Not only is the same thing true of the 

 entering sperm in the egg of Bufo, but the male pronucleus, 

 when it is about to fuse with the female pronucleus, often 

 has more pigment around it than when it was first formed 

 (PI. XXXI, Fig. 50). 



Pick believes that there are three factors at work in the 

 formation of the pigment trail. 



1. The entrance of the spermatozoon. This apparently 

 takes place so quickly that a small amount of pigment is pushed 

 in before the head of the spermatozoon. It is this pigment 

 from the peripheral layer which forms the funnel-shaped base 

 of the pigment trail (PI. XXX, Pig. 46, A). 



2. The spermatozoon exerts an attraction on the surrounding 

 pigment. 1 



3. The spermatozoon stimulates the protoplasm of the tg% 

 to produce new pigment. 



The fact that when the spermatozoon penetrates into the 

 lower part of the &%% there is no indication of a pigment trail, 

 does not invalidate this last assumption ; because the proto- 

 plasm of this portion of the o.'g'g never forms much pigment, 

 and in some eggs none at all. 



2. The Male Pronucleus. 



The sperm-head enters the egg as an apparently homogene- 

 ous structure. It soon becomes shorter and thicker, and breaks 

 up into a number of closely packed rounded granules (PI. XXX, 



1 Jordan considers that this attractive force diminishes as the spermatozoon 

 penetrates deeper into the egg, in consequence of which pigment granules are 

 discarded along the way and mark the path taken by the spermatozoon. 



